1. Field of the Invention
This invention relates to flame (fire) resistant hydraulic fluid compositions that comprise at least one ester of a halogen substituted aromatic acid, also referred to as a polyhaloaromatic ester. The esters of this invention may be used alone or in combination with one or more of the following fluids: (A) mineral oils, (B) poly-.alpha.-olefins, (C) cycloaliphatics, (D) alkylated aromatics, (E) esters of dibasic acids, (F) silicones, (G) silicate esters, (H) polyol esters, (I) polyglycols, (J) phosphate esters, or (K) organohalide compounds other than the inventive esters. This invention also comprises a method for improving the flame resistance of those materials which either are flammable or have marginal flame resistance, particularly including the above fluids.
The compositions of the present invention may also include one or more shear-stable polymers which have been found to impart additional flame resistance to the hydraulic fluid.
2. Statement of Related Art
Hydraulic fluids find use wherever there is a need to transfer pressure from one point to another in a system. Some of the many commercial applications where fluids are utilized are in aircraft, braking systems, compressors, machine tools, presses, draw benches, jacks, elevators, die-castings, plastic moldings, welding, coal mining, tube reducing machines, paper-machine press rolls, calendar stacks, metal working operations, fork lifts, automobiles, etc.
The use of fire resistant hydraulic fluids is well known in industry. They are needed in those applications where it is necessary to reduce or minimize fire and explosion hazards that may result from leaking, misting or spraying hydraulic fluids onto a hot surface. Examples of applications where fire resistant hydraulic fluids are used are in aircraft and in steel rolling mills as well as high pressure systems such as in die casting machines, hydroelectric turbines, hydraulic presses, compressors, and the like.
A widely used class of fire resistant hydraulic fluids is the phosphate esters or blends containing such, exemplified by many U.S. patents including U.S. Pat. Nos. 2,862,886; 4,370,281; and 4,645,615.
Halogenated fluids have also found use as fire resistant hydraulic fluids. These include chlorinated, brominated, as well as fluorinated types and also are exemplified by many U.S. patemts including, among others, U.S. Pat. Nos. 2,528,347; 4,577,044; and 4,596,664.
The esters of polyhaloaromatic acids useful in this invention have been used as flame-proofing materials for unrelated materials. For example, U.S. Pat. No. 4,098,708 describes the use of haloester compounds as flame retardant textile finishing agents. U.S. Pat. No. 4,298,517 and 4,397,977 disclose using haloester compounds as flame retardants for halogenated resins. There are no known references disclosing the use of esters of polyhaloaromatic acids as fire resistant hydraulic fluids per se, or as components of fire resistant hydraulic fluid compositions.
Shear-stable polymers are often added to hydraulic fluids to improve the fluids's temperature viscosity characteristics. Because of their structure and/or low molecular weight, generally below 25,000, these polymers resist degradation due to mechanical shear, such as that encountered in hydraulic pumps. A further discussion of shear-stable polymers and shear induced degradation may be found in the Kirk-Othmer Encyclopedia of Chemical Technology, Third Ed., Vol. 12 (pp. 712-733, particularly pg. 721), Vol. 14 (pp. 477-526, particularly pp. 495-6), John Wiley & Sons, New York, 1981. Also see the American Society for Testing Materials 1989 Annual Book of ASTM Standards, Section 5, Petroleum Products and Lubricants, Vols. I-III (Method D2603-76, Standard Test Method for Sonic Shear Stability of Polymer-Containing Oils and Method D3945-86, Standard Test Methods for Shear Stability of Polymer-Containing Fluids Using a Diesel Injector Nozzle) for standard methods of measuring the shear stability of blends of polymers in oils.
The misting properties of a hydraulic fluid are known to affect the fluid's fire resistance. The fire-resistance of a hydraulic fluid is commonly tested by the Factory Mutual Research Test Procedure for Less Hazardous Hydraulic Fluids, Class No. 6930. This method attempts to ignite the mist of the tested oil with a propane flame or heated metal surface. If the fluid ignites, the time required for self-extinguishment is then measured. Common polyol ester hydraulic fluids, such as trimethylol trioleate, exhibit poor or marginal performance in the Factory Mutual Test.
The misting properties of the hydraulic fluid can be modified through the addition of coalescing polymers, such as polyisobutylene, which cause larger droplet formation. This increase in droplet size is due to an increase in viscosity and the coalescence of smaller fluid droplets. When coalescing polymers are added to the same polyol ester fluid, the droplet size increases sufficiently to inhibit both the ignition and flame propogation properties of the mist to pass the Factory Mutual Test. Unfortunately, because of their relatively high molecular weight, i.e. 50,000-200,000, coalescing polymers have low shear stability. Thus, the usefulness of these polymers is limited in hydraulic fluid application because of degradation due to mechanical shear in hydraulic fluids.